A device disclosed in Patent Document 1 (JP 4082004 B2 corresponding to US 2002/0162457 A1) is known as an example of a conventional fuel vapor gas purge system. The system of Patent Document 1 supplies fuel vapor stored in a canister to an intake passage of an engine through a purge passage by opening a purge control valve and rotating a purge pump positively during an operation of the engine.
According to the system of Patent Document 1, when the purge control valve is detached from the intake passage during the positive rotation of the purge pump, a vaporized fuel may leak to outside.